The invention relates to an apparatus having an electromagnetic actuator.
An actuator of this type for operating an inlet or exhaust valve of an internal combustion engine is described in Japanese Published Patent Application No. 07 224 624. The electromagnetic actuator includes two electromagnets, an opening magnet and a closing magnet, between the pole surfaces of which an armature is arranged such that it can be moved coaxially with respect to a valve axis. The armature acts on a valve stem of the inlet or exhaust valve. Furthermore, a prestressed spring mechanism acts on the inlet or exhaust valve via the armature. Two prestressed compression springs are used as the spring mechanism, of which an upper compression spring loads the inlet or exhaust valve in the opening direction, and a lower compression spring loads the inlet or exhaust valve in the closing direction. When the electromagnets are not energized, the armature is held in an equilibrium position between the electromagnets, by the compression springs and valve springs.
In addition to an operating coil, the electromagnets each have a measurement coil. The measurement coils are arranged in the radially inner region of the operating coils. The position of the armature between the electromagnets influences the inductance of the measurement coils, by which the position of the armature can be deduced from the detected inductance values of the measurement coils. The inductance decreases in a highly non-linear manner with the distance between the armature and the measurement coils, and the measurement coils are subject to strong magnetic fields from the operating coils during operation.
Furthermore, an electromagnetic actuator for operating an inlet or exhaust valve in an internal combustion engine and having a pivoting armature is described in German Published Patent Application No. 196 28 860, which pivoting armature is mounted between two electromagnets such that it can pivot about one axis.
It is an object of the present invention to provide an apparatus having an actuator for operating an actuating element, in which the position of the armature and/or of the actuating element may be detected as accurately as possible and over a wide range during operation of the actuator.
The above and other beneficial objects of the present invention are achieved by providing an apparatus as described herein.
The present invention relates to an apparatus having an electromagnetic actuator for operating an actuating element, in particular an inlet or exhaust valve of an internal combustion engine, which includes an electromagnetic unit via which an armature which is mounted such that it may move and is operatively connected to the actuating element may be moved, and having a measurement apparatus which has at least one inductive measurement element at least for detecting a position of the armature, and in particular having a spring mechanism which acts on the actuating element.
At least one inductive measurement element may be firmly connected to the armature. The inductive measurement element, which is firmly connected to the armature and is thus moved with the armature, allows any dead band to be reduced, in which no measurement signal, or only an inaccurate, weak measurement signal, may be detected during operation. In contrast to an inductive measurement element which is attached to an electromagnet in the electromagnetic unit, the measurement element which is attached to the armature is not continuously subjected to a strong magnetic field, but moves into and out of the magnetic fields of the electromagnets, by which a large measurement signal, which may be evaluated well, may be detected at an early stage before the armature meets a pole surface of the electromagnets. Advantageous open and closed-loop control of the armature movement may be achieved on the basis of a small dead band. Furthermore, a measurement element which moves with the armature allows the position of the armature with respect to two electromagnets that are at a distance from one another to be detected, without having to attach an inductive measurement element to each electromagnet. If, in addition to the inductive measurement element which is firmly connected to the armature, at least one additional inductive measurement element is attached to the electromagnetic unit, so that at least two measurement signals may be detected, this results in a particularly accurate measurement, e.g., because correction values may be determined.
In order to achieve a measurement signal which is as large as possible and may be detected and evaluated well, the measurement element which is firmly connected to the armature is formed by a measurement coil, e.g., by a measurement coil having a number of turns.
The inductive measurement element may be at least partially fitted in the armature. The measurement element may be arranged such that it is protected against external influences, and any reduction in a contact area of the armature may be avoided, with the physical volume remaining unchanged. If, furthermore, the measurement element is fitted in the armature during production, for example, during a casting process, this furthermore allows attachment parts, assembly effort and costs to be avoided. However, it is also possible for the measurement element, which is in the form of a measurement coil, to be wound onto the armature, and this may be achieved in a physically simple manner. Furthermore, all the positively locking, force-fitting and/or integral-material connections are possible, for example, bonded joints, soldered joints, etc.
The measurement element may be arranged on one surface of the armature so that, when the armature meets a pole surface of the electromagnetic unit, the armature enters a recess in the pole surface, in which a winding of the electromagnetic unit is fitted. There is no need for any additional recesses or additional physical space.
The data detected by the measurement element may be transmitted via various data transmission devices from the moving armature to a receiving unit which is firmly connected to a housing, for example, by radio, infrared, sliding contacts, etc. However, if the armature is mounted such that it may pivot, this makes it possible to transmit data in a physically simple manner via a pivoting shaft of the armature, e.g., via data lines.